Summary
Taglines or subtitles can be included using Metafields. This can be used to show a short description for your product.
How to
Enable setting
Navigate to Theme settings > Product cards > then check "Enable product tagline"
Click save
Create metafield definition
Navigate to Settings > Custom data > Products
Click Add definition
In the name field search “Product subtitle”
Select Product subtitle then click Save
Since "Product subtitle" is using a standard metafield the handle should already be set as "descriptiors.subtitle"
Update metafield
Navigate to the product you’d like to update
Scroll to the bottom and enter in a tagline in “Product subtitle”
Click Save
Metafields can also be updated using the bulk editor